The present invention relates to heating and controlling the temperature of ultra small volumes, e.g., on the order of one picoliter (1000 cubic microns). The invention is particularly useful for rapidly heating and accurately controlling the temperature in such ultra small volumes. The present invention is particularly useful in providing means to rapidly and reversibly change and measure the change in temperature in cellular areas of microdimension, e.g., a single cell, portion of a cell, or groups of specific selected cells, The controlled heating may be carried out on cells or groups of cells within or without a living body.
The integrated heat-sensor devices of the present invention, referred to hereinafter as "thermodes", have heater portions which are heated by the passage of electrical current through an electrical resistance. The heater portion also serves as a sensor portion which measures the temperature of the heater portion facilitating controlled monitored changes in the electrical resistance of the electrical circuit containing the heater portion.
Devices to measure temperature by measuring changes in electrical resistance are known in the prior art. Examples are: U.S. Pat. Nos. 2,210,903; 2,711,650; 2,737,810; 2,779,917 and 2,938,385. Generally such devices utilize either a resistance thermometer or a thermistor as the probe, or temperature sensory element. Typically a resistance thermometer includes a metal, such as, platinum, nickel or copper or a semi-conductor material. Thermistors typically utilize a solid semi-conductor ceramic-like element, e.g., oxides of manganese, cobalt, copper, uranium, iron, zinc and magnesium.
Generally electrically conducting materials become more resistant to the passage of electrical current as temperature increases. The increase in electrical resistance is, within certain determinable limits, proportional to the increase in temperature. Thus, a temperature sensing element, or probe, may be used to determine temperature in the area of the probe by measuring increases or decreases in the electrical resistance of the probe.
To facilitate precise temperature measurement such temperature probes are typically incorporated as part of a resistance measuring circuit. If a source of constant potential is available, the measuring circuit may merely include an ammeter, the change in electrical current reflecting the change in resistance in the circuit. A resistance bridge network, for example, a meter bridge or a Wheatstone bridge, may be used. A bridge circuit allows a comparison of resistances. In such circuits the electrical resistance of the temperature probe is accurately determined by evaluating the resistance of the probe in a balanced bridge circuit and the temperature of the probe is derived from the electrical resistance of the probe. In a particularly useful embodiment, the resistance of the temperature probe is determined by instrument and directly read as temperature.
In contrast to resistance thermometers and thermistors, the present invention applies an electrical current to an electrical circuit containing a resistance to obtain a heated portion and utilizes the change of resistance of the circuit to control or monitor the heat generated.
The present invention is particularly useful in the study of cellular or membrane phenomena wherein the accurate, controlled heating of a cell or part of a cell is to be carried out. The ultra small thermode, or probe, of the present invention allows cell penetration without causing serious injury to the cell, or disruption of the cell structure or function. The study of cellular temperature response has heretofore been confined to the study of groups of large cells because of the large size of prior art probes. In the past such limitations were particularly severe in the study of vertebrate brain, spinal cord and retina cells where the vast majority of cells are smaller than about 20 microns in diameter. The present invention is particularly useful as a tool for studying the effect of heat and temperature in such small cells.
The present invention may suitably be utilized to control the temperature in patch-clamp recordings. In such applications the cooling bath may be kept cold and the membrane heated locally to allow for a good seal formation. The temperature may subsequently be varied without danger of expansion or contraction of the microscope stage which may disturb a cell-attached patch. The present device also has utility in microcalorimetry applications. For example, a thermodilution flow meter which would measure flow within capillaries may be made by heating the capillary to a specific temperature and measuring the speeds at which temperatures return to normal.
The present invention facilitates the study of temperature effects in ultra small volumes, cellular or subcellular. As used herein the term ultra small volumes means a volume less than about 1000 cubic microns. The probe portion of the present device encompasses the heating and sensing portions. Typically the probe has a diameter between about 0.5 and about 5.0 micron. It is postulated that the present invention may open research vistas not heretofore open which will encompass the study of the affects of temperature within a particular cell or particular cells within a group of cells.
The fabrication of microcapillary tubes aptly suited to use in the present invention is described in U.S. Application Ser. No. 693,725, filed Jan. 23, 1985, entitled, "METHOD AND APPARATUS FOR PRODUCING GLASS TUBING OF A NARROWED DIAMETER". Methods of applying metallic coatings to microcapillary tubes are disclosed in U.S. Pat. Nos. 4,452,249, "MICROELECTRODES AND PROCESS FOR SHIELDING SAME"; and 4,427,283, "MICROELECTRODE FABRICATING APPARATUS". The disclosures of the foregoing are hereby incorporated by reference.